ATLANTA -- The suicide rate among preteen and young teen girls spiked dramatically in a disturbing shift that federal health officials say they can't fully explain.

For all young people between ages 10 to 24, the suicide rate rose 8 percent from 2003 to 2004 _ the biggest single-year bump in 15 years _ in what one official called "a dramatic and huge increase."

The report, based on the latest numbers available, was released Thursday by the Centers for Disease Control and Prevention and suggests a troubling reversal in recent trends. Suicide rates had fallen by 28.5 percent since 1990 among young people.

The biggest increase was in the suicide rate for 10- to 14-year-old girls. There were 94 suicides in that age group in 2004, compared to 56 in 2003, a 67 percent increase. The rate is still low _ fewer than one per 100,000 population.

Suicide rates among older teen girls, those aged 15-19 shot up 32 percent; rates for males in that age group rose 9 percent.

"In surveillance speak, this is a dramatic and huge increase," Dr. Ileana Arias said of the overall picture. She is director of the CDC's National Center for Injury Prevention and Control.

More research is needed to determine whether this is a trend or just a blip, said one child psychiatrist, Dr. Thomas Cummins of Children's Memorial Hospital in Chicago. "We all need to keep our eye on this over time to see if this is a continuing trend."

Overall, there were 4,599 suicides among young people in 2004, making it the third-leading cause of death, surpassed only by car crashes and homicide, Arias said. Males committed suicide far more often than females, accounting for about three-quarters of suicides in this age group.

The study also documented a change in suicide method. In 1990, guns accounted for more than half of all suicides among young females. By 2004, though, death by hanging and suffocation became the most common suicide method. It accounted for about 71 percent of all suicides in girls aged 10-14; about half of those aged 15-19; and 34 percent between 20-24.

"While we can't say (hanging) is a trend yet, we are confident that's an unusually high number in 2004," said Dr. Keri Lubell, a CDC behavioral scientist who was one of the study authors.

Scientists speculated that hanging may have become the most accessible method.

"It is possible that hanging and suffocation is more easily available than other methods, especially for these other groups," Arias said.

The CDC is advising health officials to consider focusing suicide prevention programs on girls ages 10-19 and boys between 15-19 to reverse the trends. It also said the suicide methods suggest that prevention focused solely on restricting access to pills, weapons or other lethal means may be of limited success.

As for why rates are up, Richard Lieberman, who coordinates the suicide prevention program for Los Angeles public schools, said one cause could be a rise in depression during tumultuous adolescent years.

"There's a lot of pressure in and around middle school kids. They're kind of all transition kids. They're turbulent times to begin with," he said. "The hotline's been ringing off the hook with middle school kids experimenting with a wide variety of self-injurious behavior, exploring different ways to hurt themselves."

Arias said the declining use of antidepressants in those age groups might play a role. But it's "not the only factor" that health officials will be studying.

Four years ago, federal regulators warned that antidepressants seemed to raise the risk of suicidal behavior among young people, so black box warnings were put on the drugs' packaging.

When partial teen suicide data was published earlier this year, experts noted at the time that the drop in sales of the drugs corresponded with a rise in the suicide rate. Now there is concern that some children who need the medication aren't getting it.

"Suicide is a multidimensional and complex problem," Arias said. "As much as we'd like to attribute suicide to a single source so we can fix it, unfortunately we can't do that."

More education is needed, some specialists said, so that teachers, parents and others can quickly spot troubled teens.

"It underscores the need for more evaluation methods for school personnel and pediatricians to be able to better identify at-risk youth," said Dr. Alec Miller, director of the adolescent depression and suicide program at Montefiore Medical Center in New York. "They are out there, and everyone needs to be better trained in identification."

He said people who commit suicide tend to have a psychiatric condition, even if it has not been formally diagnosed.

Arias said warning signs include mental illness, alcohol and drug use, family dysfunction and relationship problems.

"For some, talking about suicide is awkward," she said. "Our goal is to stop suicides, and to do that we need everyone's willingness to talk about it.